diff --git a/embed/bootloader/messages.c b/embed/bootloader/messages.c
index bdf479fa07..e9be5862e7 100644
--- a/embed/bootloader/messages.c
+++ b/embed/bootloader/messages.c
@@ -318,7 +318,7 @@ static bool _read_payload(pb_istream_t *stream, const pb_field_t *field, void **
 
 static image_header hdr;
 
-extern secbool load_vendor_header_keys(const uint8_t * const data, vendor_header * const vhdr);
+secbool load_vendor_header_keys(const uint8_t * const data, vendor_header * const vhdr);
 
 secbool compare_to_current_vendor_header(const vendor_header * const new_vhdr)
 {
diff --git a/embed/extmod/modtrezorui/display.c b/embed/extmod/modtrezorui/display.c
index 7091fa5aa8..8e68966f4a 100644
--- a/embed/extmod/modtrezorui/display.c
+++ b/embed/extmod/modtrezorui/display.c
@@ -385,7 +385,7 @@ void display_print(const char *text, int textlen)
 }
 
 #ifndef TREZOR_UNIX
-extern int mini_vsnprintf(char* buffer, unsigned int buffer_len, const char *fmt, va_list va);
+int mini_vsnprintf(char* buffer, unsigned int buffer_len, const char *fmt, va_list va);
 #endif
 
 // variadic display_print
diff --git a/embed/trezorhal/common.c b/embed/trezorhal/common.c
index 9a6d05a7f3..ae9e716dc5 100644
--- a/embed/trezorhal/common.c
+++ b/embed/trezorhal/common.c
@@ -30,13 +30,6 @@ void __attribute__((noreturn)) __fatal_error(const char *expr, const char *msg,
     for (;;);
 }
 
-uint32_t __stack_chk_guard = 0;
-
-void __attribute__((noreturn)) __stack_chk_fail(void)
-{
-    ensure(secfalse, "Stack smashing detected");
-}
-
 #ifndef NDEBUG
 void __assert_func(const char *file, int line, const char *func, const char *expr) {
     __fatal_error(expr, "assert failed", file, line, func);
@@ -59,3 +52,10 @@ void clear_otg_hs_memory(void)
     memset_reg((volatile void *) USB_OTG_HS_DATA_FIFO_RAM, (volatile void *) (USB_OTG_HS_DATA_FIFO_RAM + USB_OTG_HS_DATA_FIFO_SIZE), 0);
     __HAL_RCC_USB_OTG_HS_CLK_DISABLE(); // disable USB OTG_HS peripheral clock as the peripheral is not needed right now
 }
+
+uint32_t __stack_chk_guard = 0;
+
+void __attribute__((noreturn)) __stack_chk_fail(void)
+{
+    ensure(secfalse, "Stack smashing detected");
+}
diff --git a/embed/trezorhal/common.h b/embed/trezorhal/common.h
index 1bcc86ffab..7973eb7b1c 100644
--- a/embed/trezorhal/common.h
+++ b/embed/trezorhal/common.h
@@ -4,20 +4,20 @@
 #include <stdint.h>
 #include "secbool.h"
 
-extern void memset_reg(volatile void *start, volatile void *stop, uint32_t val);
-
-void clear_otg_hs_memory(void);
-
 void __attribute__((noreturn)) __fatal_error(const char *expr, const char *msg, const char *file, int line, const char *func);
 
 #define ensure(expr, msg) (((expr) == sectrue) ? (void)0 : __fatal_error(#expr, msg, __FILE__, __LINE__, __func__))
 
-void jump_to(uint32_t address);
-
 void hal_delay(uint32_t ms);
 
-void shutdown(void);
+void clear_otg_hs_memory(void);
 
 extern uint32_t __stack_chk_guard;
 
+// the following functions are defined in util.s
+
+void memset_reg(volatile void *start, volatile void *stop, uint32_t val);
+void jump_to(uint32_t address);
+void shutdown(void);
+
 #endif
diff --git a/embed/trezorhal/stm32.c b/embed/trezorhal/stm32.c
index d243b967b4..7fe809ff8e 100644
--- a/embed/trezorhal/stm32.c
+++ b/embed/trezorhal/stm32.c
@@ -52,7 +52,7 @@ void SysTick_Handler(void)
     uwTick++;
 }
 
-extern void shutdown(void);
+void shutdown(void);
 
 void PVD_IRQHandler(void)
 {